Light emitting panel assemblies use light guides to transmit light from point light sources such as light emitting diodes (LEDs) to extraction elements where the light is extracted. Luminaires are an example of light emitting panel assemblies.
One objective in lighting is to provide even illuminance on a work plane, which can be achieved by providing a lighting distribution known in the art as a “batwing” distribution. Another objective in lighting is to eliminate or reduce glare. Glare is an effect of luminance at high vertical angles that can cause visual discomfort to users.
Luminance of a luminaire is determined by dividing luminous intensity by projected area at a particular angle.
Conventional luminaires are horizontally oriented, i.e., the luminaire is wider than it is tall. This configuration allows light to leave towards the work plane from traditional sources such as fluorescent and incandescent light sources. A challenge with this configuration is that projected area shrinks as the angle increases so increasing luminous intensity in order to provide even illuminance would create unacceptable levels of high vertical angle luminance, i.e., glare. Baffling is one measure that may be used to mitigate glare in horizontally-oriented luminaires.
Vertically oriented luminaires are advantageous because projected area is smaller at low vertical angles where less luminous intensity is required and projected area increases as the vertical angle increases, as illustrated for example in FIGS. 1 and 2A to 2D. This configuration allows luminous intensity to be higher at higher vertical angles compared to that of a horizontally oriented luminaire, avoiding the problem of glare which would otherwise require resorting to additional measures such as baffling. A challenge with this configuration is that the small projected area at low vertical angles results in high luminance at these angles, as illustrated for example in FIG. 2A. While luminaires are typically installed above users and not in their direct field of view, too much luminance at low vertical angles can still cause visual discomfort in their peripheral field of view. Minimizing luminous intensity at lower vertical angles is thus desirable for vertically oriented luminaires. Conventional light extraction elements, however, typically allow too much light to be emitted at these lower vertical angles.
Light extraction elements that optimize light distribution for vertically oriented luminaires are desirable. For certain designs of vertically oriented luminaires, it is additionally desirable for a light guide of the luminaire to be designed to emit most or all of the light from one side of the light guide.